1. Technical Field
The present invention relates generally to data storage devices within data processing systems and more particularly to a method and apparatus for alleviating elevated temperatures within data storage devices.
2. Description of Related Art
The requirement for high density magnetic storage of data on hard disk drives has been increasing steadily for the past several years. Hard disk drives include magnetic heads for reading and writing data to the hard disk. The heads include write coils and sensors for reading data from the disks. For purposes of the ensuing description of the assembly including the write coil and yoke will be referred to as the xe2x80x9cwrite coilxe2x80x9d and the assembly including the magnetoresistive sensor situated between magnetic shields will be referred to as the xe2x80x9cread sensorxe2x80x9d
Miniaturization of magnetoresistive (MR) sensors for disk drives in the early 1990""s allowed disk drive products to maximize storage capacity with a minimum number of components. Fewer components result in lower costs, higher reliability, and lower power requirements for the hard disk drives.
MR sensors are used for the read element of a read/write head. MR sensors read magnetically encoded information from the magnetic medium of the disk by detecting magnetic flux stored in the magnetic medium of the disk. As storage capacity of disk drives has increased, the storage bit has gotten smaller and its magnetic field has correspondingly become weaker. MR heads are more sensitive to weaker magnetic fields than are the inductive read coils used in earlier disk drives. Thus, the move away from inductive read coils and to MR sensors for use in disk drives.
As discussed above, MR sensors are known to be useful in reading data with a sensitivity exceeding that of inductive or other thin film sensors. However, the development of Giant Magnetoresistive (GMR) sensors (also referred to as GMR head chips) has greatly increased the sensitivity and the ability to read densely packed data. Thus, although the storage capacity for MR disks is expected to eventually reach 5 gigabits per square inch of surface disk drive (Gbits/sq.in.), the storage capacity of GMR disks is expected to exceed 100 Gbits/sq.in.
The GMR effect utilizes a spacer layer of a non-magnetic metal between two magnetic metals. The non-magnetic metal is chosen to ensure that coupling between magnetic layers is weak. GMR disk drive read sensors operate at low magnetic flux intensities. When the magnetic alignment of the magnetic layers is parallel, the GMR sensor resistance is relatively low. When the magnetic alignment of the layers is anti-parallel, the resistance is relatively high. Heat generated in the read/write head together with heat from other components within the disk drive materially affects the operating temperature of the GMR read sensor in the head.
As GMR sensors allow extremely high data densities on disk drives, a stable sensor temperature is essential to accurate read operations in high track density hard disk drives. It is well known that the signal to noise ratio of GMR read sensors increases with a decrease in temperature. Various methods of cooling hard disk drive components are known and include forced air, cooling fins, and heat pipes. Generally, the cooling methods have been limited to attaching materials or structures that have high thermal conductivities to transfer heat away from the head. However, due to space limitations and ambient conditions, means for cooling, whether to ambient or subambient temperatures, are generally not available to the GMR read sensor.
As the requirements for the GMR read sensors have been increasing over the years, the requirements for the write coils within the disk drives have also been increasing. New disk drives require fast field reversal during the write operation. This requirement for fast field reversal during the write operation implies larger write currents. Also, as the storage densities increase, the media coercivity has to increase to avoid thermal instability and the superparamagnetic limit. This reinforces the need for even larger write currents. However, large write currents increase the Joule heating in the coil such that the coil temperatures are 40 to 80 degrees Celsius above ambient temperatures. However, for optimal operation, the write coils need to be kept near ambient temperatures. Furthermore, since the write coil is immediately adjacent the GMR read sensor in the head, the heating and elevated temperatures are shared by the GMR read sensor.
Therefore, it would desirable to have a method and apparatus for cooling the GMR read sensor and the write coils in the heads of hard disk drives that would be practical and fit within the structure of the head without requiring serious structural changes to the hard disk drive. Cooling GMR read sensors would significantly enhance magnetic sensing capacity of the GMR read sensors during the read operation and increase performance of the write coils during a write operation. It would also be desirable to provide a practical method for cooling the heads to subambient temperatures that would allow the utilization of GMR materials that have significantly higher sensitivities.
The present invention provides a read/write head cooling system for use in a magnetic storage device, such as, for example, a hard disk drive. In one embodiment, a thermally conducting patterned cold plate is thermally situated between a write coil and a read sensor of the read/write head. A microcooler, such as, for example, a thermoelectric cooler, is thermally coupled to the cold plate. A hot plate of one or more heat dissipation elements, such as, for example, copper posts, is thermally coupled to the hot side of the microcooler. The write coils of the read/write head are actively cooled by the microcooler to reduce the temperature of the write coil and read sensor in the head below that attainable with passive mechanisms.